Project 4 continues to probe (1) what mutagens and other potential toxicants are in the air we breathe and (2) what is the effect of these respirable toxicants on our lungs. The major objectives of Project 4 are threefold: (1) the determination of DNA-adducts in human cell models and human lung, (2) the physico-chemical characterization of respirable particles in human lung, and (3) the detailed structural elucidation of mutagens found in respirable particles. The strategy for the determination and identification of DNA adducts has three principal parts which will take place concurrently. In the first part, we will use an existing method developed in our laboratory involving fluorescence post-labeling and capillary electrophoresis to detect DNA adducts in human lung tissue. In the second part of our work, we will extend this fluorescence post-labeling method in terms of selectivity and sensitivity and also develop laser desorption Fourier transform mass spectrometry (C0/2-LD-FTMS) as a complementary technique for detection of the fluorophore-labeled DNA adducts. The third part involves the continued adaptation of a promising method, muHPLC/FL developed during the current period of performance of this project. The measurement of DNA adducts is important for human health because lung cancer is a prevalent and virtually incurable disease and the evidence is overwhelming that DNA adducts are associated with cancer. Research on particle characterization proposed here is based on the application of an innovative method, developed at NIT, for quantification of the fine structure of carbon-based and other respirable particulate matter utilizing high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX). The tasks associated with Specific Aim 2 are organized into three main areas: (1) particle imaging in human lung by HRTEM; (2) particle characterization by EELS and EDX and (3) source identification and apportionment. Our third objective is the detailed structural elucidation of compounds sampled in Project 1 and determined in Project 2 to be important human cell mutagens. Work to date has shown that the semi-polar fraction accounts for up to one-half or more of the total mutagenicity of respirable air particles and we will be focusing our efforts on this class of mutagens. Investigators will also collaborate in the characterize respirable particles and aerosols emitted from natural gas combustors and propose to determine what components in the emissions from these combustors are responsible for the heightened mutagenicity of these samples.